Make conscript part of sbt itself

[oswaldo]

This is actually a suggestion. Just crossed my mind that the official documentation already points to conscript to achieve one of the sbt features: Scripts (kind of an interesting circular dependency going on here), so I guess it would make sense that the two projects talk to each other about this possibility.

[eed3si9n]

As it happens that I am currently a maintainer of both conscript and sbt, but the dependency from conscript to sbt is just the launcher mechanism. Plus I kind of like the fact that conscript is more narrowly focused and small. As long as the launcher doesn't change, we can keep conscript as active or stable as we want having a different life cycle from sbt's releases.